In the studies of liposomes which are delivered preferentially to tumor cells, methods for modifying liposomal surfaces with monoclonal antibodies have hitherto been reported, e.g., in Tadakuma, Iyaku Journal, Vol. 20, p. 643 (1984), Tadakuma, Saibo Kogaku, Vol. 1, p. 72 (1982), Ohsawa et al., Chemical and Pharmaceutical Bulletin, Vol. 35, p. 740 (1987), and Papahadjopoulos et al., Cancer Research, Vol. 46, p. 4,904 (1986). In particular, Ohsawa et al. reported that small unilamellar liposomes modified with anti-carcinoembryonic antigen antibodies were easily taken up by tumor cells to exhibit enhanced antitumor effects.
Under the present situation, however, the monoclonal antibodies are difficult to commercialize because of the difficulty of mass-production.